Contoured casing for an electrochemical cell

ABSTRACT

The present invention provides an electrochemical cell of either a primary or a secondary chemistry housed in a casing having opposed major side walls of a contoured shape.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority based on provisional application Ser.No. 60/306,647, filed Jul. 19, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrochemical cells generatingelectrical energy by means of chemical reactions. More specifically, theinvention relates to casings for electrochemical cells, the cells beingparticularly adapted for powering implantable devices. For that reason,the casings have contoured surfaces to more closely conform to bodycontours. This facilitates implantation in areas of a body that wereheretofore not possible because of geometrical limitations.

2. Prior Art

Recent developments in small electronic devices having various shape andsize requirements necessitate comparably small-sized electrochemicalcells that are easily manufactured and used in these electronic devices.Preferably, these types of cells are of a high energy density, such asis provided by those predicated on a lithium chemistry. One widely usedconfiguration is to house the high energy density cell in aprismatic-shaped casing 10, as shown in FIG. 1. Whether the cell is of aprimary or a secondary chemistry is not important. The casing 10includes a planar front side wall 12 opposite a planar back side wall(not shown), both of which extend to and meet with a right end wall 14and an opposed left end wall (not shown). The front and back side wallsand the right and left end walls extend to and meet with a planar bottomwall (not shown) in a unitary construction referred to as a deep drawncasing. This unitary casing design has a generally rectangular shapewith the front and back side walls being parallel to each other and theright and left end walls being parallel. An alternate construction is toprovide individual plates which are connected together as side walls andend walls to form the rectangularly-shaped prismatic casing.

In any event, the connected side walls and end walls form an openingclosed by a generally planar lid 16. The lid 16 has a rectangular shapeand is welded about its periphery to the upper edges of the respectiveside walls and end walls. The lid includes a fill opening 18 and aterminal pin opening 20. The fill opening 18 is a port for providing anelectrolyte into the casing after an electrochemical couple is housedtherein. The port is closed by a closure member, such as a ball 22,sealed therein.

The terminal pin opening 20 supports a glass-to-metal seal comprising aring of insulative glass 24 surrounding a terminal pin 26 having itsinterior end (not shown) connected to one of the anode and cathodeelectrodes housed inside the casing. That way, the terminal pin 26serves as one of the cell leads. The casing 10, insulated from theterminal pin 26 by the glass-to-metal seal 24, serves as the lead forthe other electrode.

The major draw back with the prismatic shaped casing 10 is that it isnot necessarily the most optimum or desired shape, for example when thecell is intended to be implanted into a human body, and the like. Insuch applications, a prismatic shaped housing may not represent the bestor most efficient usage of space in the body. According to the presentinvention, a casing having a contoured shaped is more preferred.

A hybrid casing construction is described in U.S. Pat. No. 5,958,088 toVu et al. This patent shows a prismatic casing having partiallycontoured side walls. The cell casing includes opposed major side walls,one having a concave arc while the other has an opposed convex arc. Thecell electrodes are disposed within the casing and deflected in a springlike manner to follow the arcs of the opposed side walls. That way, thecasing maintains a positive pressure against the cell electrodes. Theproblem is that while the opposed side walls are arced, the intermediatesurrounding end wall does not follow their contours. This makes the Vuet al. casing design impractical for implantation in the human body whena fully contoured shape is most preferred.

Accordingly, there is a need for cells housed in casings having fullycontoured side walls more closely matching the shape of the human bodythan does a prismatic casing.

SUMMARY OF THE INVENTION

Presently, primary lithium cells are used for implantable medicalapplications such as pacemakers, implantable defibrillators,neurostimulators and drug pumps, while lithium ion rechargeable cellspower hearing-assist devices, artificial hearts and heart-assistdevices. These cells are generally housed inside casings having planarside walls, such as in a prismatic casing. However, the shape of a cellpackage is critical for implantable devices since the casing's formrequires the device manufacturer to design electronics and ancillarydevices around the limiting criteria of the casing. Also, if an area ofthe body, such as the skull, must be excavated, a conventional prismaticcell case requires that the cavity be shaped to fit the planar prismaticdesign. This may necessitate more excavation than would be required ifthe casing is contoured to fit the patient's anatomy. Furthermore, theplanar design of current prismatic cases excludes certain locations inthe body from having medical devices implanted therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conventional prismatic casing 10.

FIG. 2 is a schematic cross-sectional view of a casing having opposedmajor curved side walls of a radius R₁.

FIG. 3 is a schematic cross-sectional view of a casing having opposedmajor curved side walls of varying radii R₂ to R₄.

FIG. 4 is a schematic cross-sectional view of a casing having opposedmajor curved side walls of varying radii R₅ to R₆ with intermediateplanar sections.

FIG. 5A is an exploded view of one embodiment of a contoured deep drawncell casing 30 according to the present invention.

FIG. 5B is a side elevational view of the casing 30 shown in FIG. 5A.

FIG. 6A is an exploded view of another embodiment of a contoured deepdrawn cell casing 70 according to the present invention.

FIG. 6B is a side elevational view of the casing 70 shown in FIG. 6A.

FIG. 7 is a perspective view of contoured clam shell casing halves 112and 114 for another embodiment of a contoured casing 110.

FIG. 8 is a perspective view of a contoured winding mandrel.

FIG. 9 is a perspective view of a wound cell stack using the windingmandrel shown in FIG. 8.

FIG. 10 is a perspective view of a contoured wound cell stack for usewith the contoured casing 30 shown in FIGS. 5A and 5B.

FIG. 11 is a perspective view of the contoured wound cell stack of FIG.10 being inserted into the casing 30 of FIG. 5A.

FIG. 12 is a perspective view of another embodiment of a contoured woundcell stack for use with the contoured casing 70 shown in FIGS. 6A and6B.

FIG. 13 is a perspective view of another embodiment of a contouredcasing 270 according to the present invention having a front side wall272 of a greater radial curvature than a back side wall 274.

FIG. 14 is an elevational view of another embodiment of a cell 290according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The casings of this invention are preferably of conductive materialsselected from nickel, aluminum, stainless steel, mild steel, tantalumand titanium.

Referring now to FIGS. 2 to 4, there is shown representative schematiccross-sectional views of casings having contoured or curved opposedmajor side walls according to the present invention. In FIG. 2, thecasing 30 comprises spaced apart and opposed major first and second sidewalls 32 and 34, each of a curvature defined by the radius R₁ movingalong a path from tangent point 36 to tangent point 38. The radius R₁ isnot shown for the second side wall 34, however, it is the same as thatof the first side wall 32. The side walls 32, 34 extend to curved endwalls 40 and 42 and a bottom wall (not shown). As will be explained indetail hereinafter, the casing 30 is closed by a lid (not shown).

FIG. 3 shows another embodiment of a casing 50 comprising spaced apartand opposed major first and second curved sidewalls 52 and 54. The firstmajor side wall 52 is comprised of a first curved portion 56 defined byradius R₂ moving along a path from tangent point 58 to tangent point 60where the side wall transitions to a second curved portion 62 defined byradius R₃ moving along a path from tangent point 60 to tangent point 64.At tangent point 64, the second curved portion 62 transitions to a thirdcurved portion 66 defined by radius R₄ moving along a path from tangentpoint 64 to tangent point 68.

As the drawing shows, the length of the radius R₂ is less than that ofboth R₃ and R₄ while the length of radius R₄ is less than that of R₃.The second major side wall 54 is similar in its contoured or curvedshape. The side walls 52 and 54 extend to curved end walls 70 and 72 anda bottom wall (not shown). The casing 50 is then closed by a lid (notshown).

It is within the scope of the present invention that the arrangement ofthe respective curved portions 56, 62 and 66 can be rearranged in anysequence or manner. Also, there can be only two different curvedportions in a side wall or more than three. The exact number and theirarrangement is only limited by the parameters of the particularapplication in which the electrochemical cell will be used.

FIG. 4 shows another embodiment of a casing 80 comprising spaced apartand opposed major first and second curved sidewalls 82 and 84 accordingto the present invention. The first major side wall 82 is comprised of afirst curved portion 86 defined by radius R₅ moving along a path fromtangent point 88 to tangent point 90 where the side wall transitions toa first planar or straight portion 92. The first planar portion 92 thentransitions to a second curved portion 94 defined by radius R₆ movingalong a path from tangent point 96 to tangent point 98. At tangent point98, the side wall 82 transitions to a second planar portion 100 which,in turn, transitions to a third curved portion 102 defined by radius R₇moving along a path from tangent point 104 to tangent point 106.

As the drawing shows, the lengths of radii R₅, R₆ and R₇ are equal.However, as described above with respect to FIG. 3, that is notnecessary. The lengths of planar portions 92 and 102 are equal, however,that is also not necessary. There can be more or less than two planarportions in a side wall and they can be continuous and angled withrespect to each other or separated from each other by one or more curvedportions.

Again, the second major side wall 84 is similar in shape to the firstside wall 82. The side walls 82 and 84 extend to curved end walls 108and 110 and a bottom wall (now shown). The casing 80 is then closed by alid (not shown).

Turning to FIGS. 5A, 5B, 6A, 6B and 7, these drawings show respectivecontoured casings 120, 160 and 200 according to the present invention.In particular, casings 120 and 160 are of a deep drawn constructionwhile casing 200 is of mating clam shells.

The casing 120 illustrated in FIGS. 5A and 5B includes spaced apart andopposed major front and back side walls 122 and 124 extending to andmeeting with curved right and left end walls 126 and 128. The side walls122, 124 and end walls 126, 128 are connected to a planar bottom wall130 forming the casing as a unitary, deep drawn member. Both of themajor front and back side walls 122, 124 have a curved shape of acontinuous radius deflecting in a similar direction and extending fromthe right and left end walls 126, 128. The curvatures of the front andback side walls 122, 124 are the same, although that is not necessary.As will be described in detail hereinafter, in some casing designs itmay be beneficial to provide one or the other of the front and back sidewalls having a greater curvature than the other. For example, it may beuseful to provide the front wall 122 with a greater curvature than theback wall 124. This would optimize casing internal volume whilemaintaining casing curvature for implantation purposes and the like.

The side walls and end walls of the deep drawn casing 120 form anopening 132 closed by a generally planar lid 134. Lid 134 has aperipheral shape matching that of the opening 132 and formed of aconcave edge 136 opposite a convex edge 138, both of which extend to andmeet with curved right and left edges 140 and 142. That way, when thelid 134 is secured to the upper edges of the casing side walls and endwalls, the opening 132 is closed in a hermetic manner.

The lid includes a fill opening 144 and a terminal pin opening 146. Thefill opening 144 is a port for providing an electrolyte into the casingafter an electrochemical couple is housed therein and is closed by aclosure member, such as a ball 148, sealed therein.

The terminal pin opening 146 supports a glass-to-metal seal comprising aring of insulative glass 150 surrounding a terminal pin 152 having itsinterior end (not shown) connected to one of the anode and cathodeelectrodes housed inside the casing. That way, the terminal pin 152serves as one of the electrode leads. The casing 120, insulated from theterminal pin 152 by the glass-to-metal seal 150, serves as the lead forthe other electrode.

FIGS. 6A and 6B illustrate another embodiment of a contoured casing 160including spaced apart and opposed major front and back side walls 162and 164 extending to and meeting with planar right and left end walls166 and 168. The side walls 162, 164 and end walls 166, 168 areconnected to a curved bottom wall 170 forming the casing as a unitary,deep drawn member. Both of the major front and back side walls 162, 164have a curved shape of a continuous radius deflecting in a similardirection and extending from the planar right and left end walls 166,168. The curvatures of the front and back side walls 162, 164 are thesame, however, as discussed with respect to casing 120, that is notnecessary.

The side walls and end walls of the deep drawn casing 160 form anopening 172 closed by a generally planar lid 174. Lid 174 has aperipheral shape matching that of the opening 172 and formed of aconcave edge 176 opposite a convex edge 178, both of which extend to andmeet with straight right and left edges 180 and 182. That way, when thelid 174 is secured to the upper edges of the casing side walls and endwalls, the opening 172 is closed in a hermetic manner.

As with the casing 120 of FIGS. 5A and 5B, the lid 174 includes a fillopening 184 and a terminal pin opening 186. The fill opening 184 is usedto provide an electrolyte into the casing after an electrochemicalcouple is housed therein, and is sealed closed with a ball 188.

The terminal pin opening 186 supports a glass-to-metal seal comprising aring of insulative glass 190 surrounding a terminal pin 192 having itsinterior end (not shown) connected to one of the anode and cathodeelectrodes housed inside the casing. That way, the terminal pin 192serves as one of the electrode leads. The casing 120, insulated from theterminal pin 192 by the glass-to-metal seal 190, serves as the lead forthe other electrode.

FIG. 7 illustrates another embodiment of a contoured casing 200according to the present invention. The casing has first and second clamshell portions 202 and 204 mated together and sealed about theirperiphery to provide a hermetic enclosure for an electrode assembly. Thefirst clam shell 202 has a surrounding wall comprised of spaced apartside walls 206 and 208 extending to and meeting with spaced apart endwalls 210 and 212. The side walls 206, 208 and the end walls 210, 212meet each other at rounded corners and extend to a curved front wall 214of a generally concave shape. Opposite the front wall 214 is acontinuous edge 216 of the side walls 206, 208 and end walls 210, 212.

The second clam shell 204 has a surrounding wall comprised of spacedapart side walls 218 and 220 extending to and meeting with spaced apartend walls 222 and 224. The side walls 218 and 220 and end walls 222 and224 meet at rounded corners and extend to a curved front wall 226 of agenerally concave shape. Opposite the front wall is a continuous edge228 of the side walls 218, 220 and end walls 222, 224.

The clam shells 202 and 204 are sized such that one of them has its sidewalls and end walls of a somewhat shorter length than those of theother. That way, after an electrochemical couple is nested in the oneclam shell having the shorter side walls and end walls, the other clamshell is mated thereto. In this position, the shorter side walls and endwalls are received in a closely spaced relationship partially covered bythe somewhat longer side walls and end walls of the other clam shell.The one continuous edge 216, 228 of the larger clam shell is thensecured to the side walls and end walls of the other clam shell, such asby welding. This provides a hermetic closure for the casing 220 havingthe major concave walls 214, 226 spaced from one another but of asimilar curvature deflecting in a similar direction. While not shown inthe drawing, the cell is provided with an electrolyte fill opening and aterminal pin insulated from the casing by a glass-to-metal seal, in asimilar manner as the previously described cells 120, 160.

It is also within the scope of the present invention that the clamshells are butted together before they are sealed. This means thatinstead of the side walls and end walls of one of the clam shells beingshorter than those of the other, they are of equal lengths. The buttededges are sealed together such as by welding to form a hermeticenclosure.

FIG. 8 illustrates a winding mandrel 230 for forming a wound cell stackhaving a contoured shape suitable for housing in the casing 120. Themandrel 230 includes a shaft 232 secured to a contoured plate 234. Thecontoured plate 234 comprised spaced apart first and second curved faces(only face 236 shown) extending to and meeting with curved ends 238 and240. Preferably, the curvatures of the first and second faces deflect ina similar direction and are substantially similar to that of the frontand back side walls 122, 124 of the casing 120, the front and back walls162, 164 or casing 160 and the curved walls 214 and 226 of casing 200.

FIG. 9 illustrates use of the winding mandrel 230 to provide anelectrode assembly as a wound cell stack for housing in the casing 120.The cell stack has a negative electrode structure, preferably in sheetform, comprising an anode active material for a primary cell or an anodematerial capable of intercalating and deintercalating an anode activematerial for a secondary cell. The negative electrode sheet is overlayedon top of a positive electrode structure, preferably in sheet form,comprising a cathode active material for either a primary or a secondarycell. The negative and positive electrodes are prevented from directphysical contact with each other by the provision of a separatormaterial disposed there between. A preferred electrode active sheet isdescribed in U.S. Pat. No. 5,435,874 to Takeuchi et al., U.S. Pat. No.5,571,640 to Takeuchi et al. and U.S. Pat. No. 6,174,622 to Thiebolt,III et al., all of which are assigned to the assignee of the presentinvention and incorporated herein by reference.

For the sake of clarity, the drawing of the cell stack being wound inFIG. 9 depicts only one of the negative and positive electrodes. Thedepicted electrode comprises an active material 240 contacted to acurrent collector 242 and contained inside of a separator envelope 244.Which one of the electrodes is depicted is not important as they areboth essentially the same in their general physical construction. A tab246 extends from one of the electrodes, preferably the positiveelectrode.

FIG. 10 illustrates the final shape of the wound cell stack 248 for acontoured casing according to the present invention. The cell stack 248includes a tab 250 extending from the other electrode, preferably thenegative electrode. That way, when the wound cell stack is housed insideone of the deep down casings 120 (FIG. 11) or 160 (FIG. 6A) or in thecasing 200 of mating clam shells 202, 204 shown in FIG. 7, the negativeelectrode tab 250 is connected to the casing while the positiveelectrode tab 246 is connected to the terminal pin. This provides theresulting cell in a case-negative design with the casing being thenegative terminal and the pin being the positive terminal. If a casepositive configuration is desired, the electrode configuration isreversed with the positive electrode tab 250 being connected to thecasing and the negative electrode tab 246 being connected to theterminal pin. An important aspect of the present invention is that thewinding mandrel conforms the cell stack to the shape of the casing. Thatway, when the cell stack is housed therein, there is no pressure on thecell stack other than that attributed to the anode and cathode electrodebeing wound together.

FIG. 12 illustrates another configuration of a wound cell stack 252according to the present invention. This cell stack is formed by takinga relatively long structure of one of the electrodes 254, for example,the anode, and folding it into a serpentine-like structure. Plates ofthe other electrode 256, for example, the cathode, are then interweavedbetween the folds of the anode electrode 256. For a more detaileddescription of this type of electrode assembly, reference is made toU.S. Pat. No. 4,964,877 to Keister et al, which is assigned to theassignee of the present invention and incorporated herein for reference.

As is the case with the cell stack 248, the cell stack 252 includes atab 258 for the positive electrode and a tab 260 for each one of thecathode plates. The cathode tabs 260 are connected to a bus 262, which,in turn, connects to a terminal pin (not shown). The cell stack is thenhoused inside a casing according to the present invention.

FIG. 13 illustrates another embodiment of a contoured casing 270 havingspaced apart and opposed major front and back side walls 272 and 274extending to and meeting with curved right and left end walls 276 and278. The side walls 272, 274 and end walls 276, 278 connect to a bottomwall (not shown) forming the casing as a unitary member, deep drawnmember. Both of the major front and back side walls 272, 274 have acurved shape of a continuous radius deflecting in a similar directionand extending from the end walls 276, 278. However, the curvature offront wall 272 is less than that of back wall 274. This means that theradius of the front wall 272 is greater than the radius of the back wall274.

The sidewalls and end walls of the deep drawn casing 270 form an opening280 closed by a lid 282. Lid 282 has a peripheral shape matching that ofthe opening 280. When the lid is secured to the upper edges of thecasing, the opening 280 is closed. The lid also includes an electrolytefill opening 284 and a terminal pin opening 286. The fill opening isclosed by ball 288 while the terminal pin opening 286 supports a ring ofinsulation glass 290 surrounding a terminal pin 292 for one of the anodeand the cathode. The casing 270 serves as the terminal for theelectrode.

FIG. 14 illustrates another embodiment of a contoured casing 290 havingspaced apart and opposed major front and back side walls 292 and 294.The walls 292, 294 each have a generally semicircular shape with aplanar upper edge. The walls 292, 294 extend to and meet with asemicircular intermediate end wall 296 that curves to meet them alongtheir entire radial perimeter. The side walls 292, 294 and end wall 296form the casing as a unitary member, deep drawn member. Both of themajor front and back side walls 292, 294 have a curved shape of acontinuous radius deflecting in a similar direction and extending fromthe end wall 296.

The side walls and end wall of the deep drawn casing 290 form an openingclosed by a lid 298. The lid also includes an electrolyte fill opening284 closed by ball 300 and a terminal pin opening supporting a ring ofinsulation glass 302 surrounding a terminal pin 304 for one of the anodeand the cathode. The casing 290 serves as the terminal for theelectrode. For a more detailed description of this type of cell,reference is made to U.S. Pat. No. 5,905,001 to Elliott et al., which isassigned to the assignee to the present invention and incorporatedherein by reference.

The previously described cell stacks 248, 252 are of either an alkalimetal/solid cathode or alkali metal/oxyhalide chemistry of both solidcathode and liquid electrolyte types. In the primary solid cathode type,for example a lithium-solid cathode cell, a solid cathode activematerial such as silver vanadium oxide or copper silver vanadium oxide,is contained within the contoured casing and surrounded by a separator,such as of a polypropylene fabric or cloth. Contemplated solid cathodeactive materials are not limited to silver vanadium oxide and coppersilver vanadium oxide, but, can also be manganese dioxide, cobalt oxide,nickel oxide, copper oxide, copper sulfide, iron sulfide, irondisulfide, titanium disulfide, copper vanadium oxide, and mixturesthereof. Lithium is preferred as the anode active material.

In the liquid cathode/electrolyte or catholyte type cell, for example alithium-oxyhalide cell, liquid catholyte fills the casing interior andis in operative contact with the anode electrode and with the cathodeelement comprising the current collector 152 sandwiched between opposedcarbonaceous plates. A separator is disposed between the anode and thecarbonaceous cathode. For a more detailed description of such a cellreference is made to U.S. Pat. No. 4,246,327 to Skarstad et al., whichis assigned to the assignee of the present invention and incorporatedherein by reference.

By way of example in an illustrative primary cell, the cathode activematerial is a silver vanadium oxide material as described in U.S. Pat.Nos. 4,310,609 and 4,391,729 to Liang et al., or copper silver vanadiumoxide as described in U.S. Pat. Nos. 5,472,810 and 5,516,340 to Takeuchiet al., all assigned to the assignee of the present invention andincorporated herein by reference. The cathode current collector is oftitanium and terminal lead 152, 192 is of molybdenum, the electrolyte isa 1.0M to 1.4M solution of LiAsF₆ or LiPF₆ in a 50:50 mixture of, byvolume, 1,2-dimethoxyethane and propylene carbonate, glass seal 58, 98is of TA-23 Hermetic sealing glass, and closure means 148, 188 is ofstainless steel. The lithium anode is preferable in sheet form contactedto both sides of a nickel foil current collector.

In a secondary electrochemical cell, the anode or negative electrodecomprises an anode material capable of intercalating andde-intercalating the anode active material, such as the preferredlithium. A carbonaceous negative electrode comprising any of the variousforms of carbon (e.g., coke, graphite, acetylene black, carbon black,glass carbon, “hairy carbon” etc.) which are capable of reversiblyretaining the lithium species is preferred. A “hairy carbon” material isparticularly preferred due to its relatively high lithium-retentioncapacity. “Hairy carbon” is a material described in U.S. Pat. No.5,443,928 to Takeuchi et al., which is assigned to the assignee of thepresent invention and incorporated herein by reference. Graphite isanother preferred material. Regardless of the form of the carbon, fibersof the carbonaceous material are particularly advantageous because theyhave excellent mechanical properties which permit them to be fabricatedinto rigid electrodes that are capable of withstanding degradationduring repeated charge/discharge cycling. Moreover, the high surfacearea of carbon fibers allows for rapid charge/discharge rates.

Also in secondary systems, the positive electrode preferably comprises alithiated material that is stable in air and readily handled. Examplesof such air-stable lithiated cathode active materials include oxides,sulfides, selenides, and tellurides of such metals as vanadium,titanium, chromium, copper, molybdenum, niobium, iron, nickel, cobaltand manganese. The more preferred oxides include LiNiO₂, LiMn₂O₄,LiCoO₂, LiCo_(0.92)Sn_(0.08)O₂ and LiCo_(1−x)Ni_(x)O₂.

A preferred electrolyte for a secondary cell is described in U.S.application Ser. No. 09/669,936, which is assigned to the assignee ofthe present invention and incorporated herein by reference.

It is appreciated that various modifications to the present inventiveconcepts described herein may be apparent to those of ordinary skill inthe art without departing from the spirit and scope of the presentinvention as defined by the herein appended claims.

1. An electrochemical cell, which comprise: a) a negative electrode; b)a positive electrode; c) a casing housing the negative and positiveelectrodes, wherein the casing comprises spaced apart first and secondmajor side walls extending to and meeting with opposed third and fourthend walls, the first and second major side walls and the third andfourth end walls extending from a bottom wall to an open end closed by alid, and wherein the first and second major side walls are continuouslycurved about their entire extent and in a similar direction from wherethey connect to the third end wall to where they connect to the fourthend wall and from the bottom wall to the open end, wherein at least oneof the first and second major side walls has a first curvature portiontransitioning into a second, different curvature portion and whereinboth the first and second curvature portions deflect in a similardirection; and d) an electrolyte provided in the casing to activate thenegative and positive electrodes.
 2. The electrochemical cell of claim 1wherein at least one of the first and second curvature portions of thefirst major side wall is of a greater curvature than at least a portionof the second major side wall.
 3. The electrochemical cell of claims 1wherein the third and fourth end walls are curved.
 4. Theelectrochemical cell of claim 1 wherein the third and fourth end wallsare generally planar.
 5. The electrochemical cell of claim 1 wherein thelid supports an electrolyte fill opening.
 6. The electrochemical cell ofclaim 1 wherein the lid supports a terminal lead for one of the negativeand the positive electrodes.
 7. The electrochemical cell of claim 6wherein the terminal lead is connected to the positive electrode and thecell is built in a case-negative configuration.
 8. The electrochemicalcell of claim 6 wherein the terminal lead is connected to the negativeelectrode and the cell is built in a case-positive configuration.
 9. Theelectrochemical cell of claim 1 of either a primary or a secondarychemistry.
 10. The electrochemical cell of claim 1 of a primarychemistry with the positive electrode of a cathode active materialselected from the group consisting of silver vanadium oxide, coppersilver vanadium oxide, manganese dioxide, cobalt oxide, nickel oxide,copper oxide, copper sulfide, iron sulfide, iron disulfide, titaniumdisulfide, copper vanadium oxide, and mixtures thereof.
 11. Theelectrochemical cell of claim 1 of a secondary chemistry with thepositive electrode of a cathode active material selected from the groupconsisting of LiNiO₂, LiMn₂O₄, LiCoO₂, LiCo_(0.92)Sn_(0.08)O₂,LiCo_(1−x)Ni_(x)O₂, and mixtures thereof.
 12. The electrochemical cellof claim 1 of a secondary chemistry with the negative electrode of ananode material selected from the group consisting of coke, graphite,acetylene black, carbon black, glassy carbon, hairy carbon, and mixturesthereof.
 13. The electrochemical cell of claim 1 wherein the negativeand positive electrodes are provided in a wound cell stack.
 14. Theelectrochemical cell of claim 1 wherein one of the negative and positiveelectrodes is folded in a serpentine-like structure with plates of theother of the negative and positive electrodes received in the folds. 15.The electrochemical cell of claim 1 wherein the casing is of a materialselected from the group consisting of nickel, aluminum, stainless steel,mild steel, tantalum, and titanium.
 16. The electrochemical cell ofclaim 1 wherein the bottom wall is either planar or curved.
 17. Theelectrochemical cell of claim 1 of a lithium-oxyhalide chemistry havinga carbonaceous cathode current collector.
 18. An electrochemical cell,which comprise: a) a negative electrode; b) a positive electrode; c) acasing housing the negative and positive electrodes, wherein the casingcomprises spaced apart first and second major side walls extending toand meeting with an intermediate wall, the first and second major sidewalls and the intermediate wall extending to an open end closed by alid, and wherein the first and second major side walls are continuouslycurved about their entire extent and in a similar direction from whereeach of them meets the intermediate wall to the open end, wherein atleast one of the first and second major side walls has a first curvatureportion transitioning into a second, different curvature portion andwherein both the first and second curvature portions deflect in asimilar direction; and d) an electrolyte provided in the casing toactivate the negative and positive electrodes.
 19. The electrochemicalcell of claim 18 wherein at least one of the first and second curvatureportions of the first major side wall is of a greater curvature than atleast a portion of the second major side wall.
 20. The electrochemicalcell of claim 18 wherein the lid supports an electrolyte fill opening.21. The electrochemical cell of claim 18 wherein the lid supports aterminal lead for one of the negative and the positive electrodes. 22.The electrochemical cell of claim 18 of either a primary or a secondarychemistry.
 23. The electrochemical cell of claim 18 wherein theintermediate wall is either planar or curved.
 24. The electrochemicalcell of claim 18 of a lithium-oxyhalide chemistry having a carbonaceouscathode current collector.
 25. A casing for an electrochemical energystorage device, the casing comprising: a) spaced apart first and secondmajor side walls extending to and meeting with opposed third and fourthend walls, the first and second major side walls and the third andfourth end walls extending from a bottom wall to an open end, whereinthe first and second major side walls are continuously curved abouttheir entire extent and in a similar direction from where they connectto the third end wall to where they connect to the fourth end wall andfrom the bottom wall to the open end, wherein at least one of the firstand second major side walls has a first curvature portion transitioninginto a second, different curvature portion and wherein both the firstand second curvature portions deflect in a similar direction; and b) alid closing the open end.
 26. The casing of claim 25 wherein the firstsidewall is of a greater curvature than the second sidewall.
 27. Thecasing of claim 25 wherein the third and fourth end walls are curved.28. The casing of claim 25 wherein the third and fourth end walls arecurved opposite to each other.
 29. The casing of claim 25 wherein thecasing is of a material selected from the group consisting of nickel,aluminum, stainless steel, mild steel, tantalum, and titanium.
 30. Thecasing of claim 25 wherein the bottom wall is either planar or curved.31. A casing for an electrochemical energy storage device, the casingcomprising: a) spaced apart first and second major side walls extendingto and meeting with an intermediate wall, the first and second majorside walls and the intermediate wall extending to an open end, whereinthe first and second major side walls are continuously curved abouttheir entire extent in a similar direction from where they meet theintermediate wall to the open end, wherein at least one of the first andsecond major side walls has a first curvature portion transitioning intoa second, different curvature portion and wherein both the first andsecond curvature portions deflect in a similar direction; and b) a lidclosing the open end.
 32. The casing of claim 31 wherein at least one ofthe first and second curvature portions of the first major side wall isof a greater curvature than at least a portion of the second major sidewall.
 33. The casing of claim 31 wherein the intermediate wall is eitherplanar or curved.
 34. A method for providing an electrochemical cell,comprising the steps of: a) providing a casing comprising spaced apartfirst and second major side walls extending to and meeting with opposedthird and fourth end walls, the first and second major side walls andthe third and fourth end walls extending from a bottom wall to an openend, wherein the first and second major side walls are continuouslycurved about their entire extent and in a similar direction from wherethey connect to the third end wall to where they connect to the fourthend wall and from the bottom wall to the open end, wherein at least oneof the first and second major side walls has a first curvature portiontransitioning into a second, different curvature portion and whereinboth the first and second curvature portions deflect in a similardirection; b) housing a negative electrode and a positive electrodeinside the casing through the open end; c) connecting the negative andpositive electrodes to respective terminals; d) closing the open endwith a lid; e) activating the negative and positive electrodes with anelectrolyte provided in the casing through a fill opening in the lid orthe casing; and f) sealing the fill opening.
 35. The method of claim 34including providing at least one of the first and second curvatureportions of the first major side wall being of a greater curvature thanat least a portion of the second major side wall.
 36. The method ofclaim 34 including providing the bottom wall being either planar orcurved.
 37. A method for providing an electrochemical cell, comprisingthe steps of: a) providing a casing comprising spaced apart first andsecond major side walls extending to and meeting with an intermediatewall, the first and second major side walls and the intermediate wallextending to an open end, wherein the first and second major side wallsare continuously curved about their entire extent and in a similardirection from where they meet the intermediate wall to the open end,wherein at least one of the first and second major side walls has afirst curvature portion transitioning into a second, different curvatureportion and wherein both the first and second curvature portions deflectin a similar direction; b) housing a negative electrode and a positiveelectrode inside the casing through the open end; c) connecting thenegative and positive electrodes to respective terminals; d) closing theopen end with a lid; e) activating the negative and positive electrodeswith an electrolyte provided in the casing through a fill opening in thelid or the casing; and f) sealing the fill opening.
 38. The method ofclaim 37 including providing at least one of the first and secondcurvature portions of the first major side wall being of a greatercurvature than at least a portion of the second major side wall.
 39. Themethod of claim 37 including providing the intermediate wall beingeither planar or curved.